1. Field of the Invention
The invention relates generally to a read/write head positioning system used in magnetic data storage devices, such as computer hard drives, and, more specifically, to a method of marking servo tracks in a way that expedites the servo writing process.
2. Description of the Related Art
Hard disk drives are commonly available memory storage devices. The typical hard disk drive includes a plurality of disks having surfaces of magnetic media that are rotating at high speeds about a spindle. A plurality of pivotable head assemblies are mounted with respect to the disk surfaces such that the combination of the rotation of the disks and the pivoting of the head assemblies allow a transducer or head to be positioned adjacent substantially all of the surface of the disk upon which data can be recorded.
Data is typically recorded by inducing the head to produce an electromagnetic field when in proximity to the disk surface so as to change the magnetic state of the disk. Typically, the head is positioned at a particular radial location and data is recorded in a generally circular data track. Similarly, when previously recorded data is being retrieved from the disk surface, the head is positioned adjacent the disk at the radial location containing the data, and the changing magnetic state of the disk surface is then detected by the head.
Increasingly, data tracks are being positioned closer and closer together so as to increase the amount of data that can be stored on a disk surface. In some implementations, the density of data tracks can be 35,000 tracks per inch or higher. As such, it is necessary for the control system of the hard drive to be able to identify the track and the region of the track that the head is positioned adjacent.
More specifically, as data tracks are positioned very close together, it is necessary for hard drive to be able to determine the location of the heads to ensure that the heads are properly positioned with respect to data tracks in order to write and read data to and from the appropriate track. To accomplish this, the magnetic media is also programmed to have servo tracks that provide servo signals to a servo control system that provides information as to the relative position between the heads and the tracks of the hard disks.
Servo tracks are typically arranged into concentric circles positioned around the middle of the disk at a multitude of radii. In an embedded servo system, these servo tracks are split into xe2x80x9cwedgesxe2x80x9d spaced apart circumferentially at regular intervals. The hard disk manufacturer usually writes the servo tracks using a servo writer machine before any data tracks are written. Data tracks are subsequently written onto open areas on the disk surface adjacent the servo wedges such that the servo control system can determine the location of the head with respect to the data track from the positional information contained in the servo track.
Thus, in the typical embedded servo system, the head reads the servo track as it reads data, and the relation between an individual servo track and an individual data track allows the controller to calculate a position error signal (PES) and provide a correction current to the actuator. The correction current pivots the actuator in order to maintain the head""s position over the desired track. Servo wedges are also detected during seek operations to monitor the location of the head when moving between tracks.
The servo wedges are written on the disk surfaces during the manufacturing process of the hard disk drive. Typically, the hard disk drive is positioned within a servo writing machine that then induces the disks to rotate and signals are sent to the head at appropriate intervals to record the servo wedges on the disk surfaces. In general, servo writing is a time consuming process that can take up to 10 hours to write all of the servo wedges on all of the servo tracks for a single drive. As such, servo writing comprises a significant portion of the time and cost to produce a hard drive.
Servo wedges can be written one wedge at a time, however, this is particularly time consuming and adds to the time and cost to fabricate the hard drive. Moreover, writing wedges,one at a time may result in the a set of wedges not being written before the servo disks: have rotated to the next circumferential wedge location. As such, writing wedges one at a time may require that the servo writer permit the wedges to rotate to the desired position without writing wedges during this period. This can further reduce the throughput of the servo writing process.
Various techniques have been used in order to expedite the servo writing process. For example, servo writers often implement a bank writing process whereby all the heads of the servo drive are simultaneously provided current to write servo wedges. Since the heads are typically coupled together, they are all positioned at a corresponding radial and circumferential position on the different disk surfaces. Consequently, an entire bank of servo wedges can thus be written on the plurality of disk surfaces. This process can be repeated circumferentially about a servo track for each of the servo wedges of the track until the track is completed. The actuator can move the heads to a different radial position and then repeat this process for each of the servo tracks of the disk surfaces.
While bank writing expedites the servo writing process, improvements in magnetic media have begun to limit the ability of the hard disk drive manufacturers to simultaneously write entire banks of servo wedges at one time. As is understood, to write a servo wedge, current must be sourced to each of the heads writing the wedge. The amount of current needed is, of course, dependent upon the magnitude of the magnetic field needed to be produced by the head to magnetically record the servo wedge of the disk surface.
Increasingly, the magnetic media being used to fabricate the disk surface is less sensitive to magnetic fields and, consequently, stronger magnetic fields have to be generated by the head in order to write the servo wedges. However, since the head assembly and head electronics that are being built into the disk drive are being used to write the servo wedges, the ability to source these greater currents are limited by the current carrying limitations within the head electronics.
To reduce both the cost of the disk drive and the size, the electronics, such as the pre-amp typically have design constraints directed towards normal operation of the hard disk drive, e.g., only single write and read steps being performed at a time. These types of head electronics are therefore less able to handle the simultaneous application of large servo wedge writing currents being sourced to multiple heads. Consequently, the servo writing process is becoming a greater manufacturing bottleneck thereby increasing the overall cost of the hard disk drive.
Hence, there is a need for an improved process of servo writing that allows for greater throughput in the servo writing process. To this end, there is a need for a servo writing process that allows for faster servo writing even with new magnetic media that require higher amplitude magnetic fields to write the servo wedges.
The aforementioned needs are satisfied by the method of writing servo tracks of the present invention, which involves simultaneously writing portions of servo tracks to thereby expedite the servo writing process.
In one aspect the method involves writing a plurality of servo tracks (x) each having a number of servo wedges on a plurality of disk surfaces. The corresponding servo wedges on each of the plurality of disk surfaces comprise a servo wedge set (z). A first step of the method comprises writing a subset (y) of a servo wedge set (z) for a servo track (x) on a subset of the disk surfaces such that the subset (y) is being written at one time. Then, a second step begins upon completion of the first step, wherein the next subset (y) of the servo wedge set (z) on the next subset of disk surfaces is written such that the next subset (y) is being written at one time. Next, a third step involves repeating, if necessary, the first two steps until all of the servo wedges of the servo wedge set (z) have been written. In step four, the next servo wedge set (z) is moved to. Then, following step four, step five begins in which steps one through three are repeated until all of the servo wedges of the next servo wedge set (z) have been written. Subsequently, in step six, steps four and five are repeated until all of the servo wedge sets (z) of the servo track (x) have been written. Next, following step six, step seven involves moving to the next servo track (x). Step eight requires that steps one through six are repeated, if necessary, for the next servo track (x). Finally, step nine involves repeating acts seven and eight, if necessary, for each servo track (x).
Another aspect of the method involves writing servo tracks comprised of circumferentially spaced servo wedges at a plurality of radial locations on a hard drive having a plurality of disk surfaces and read write heads. The method comprises a first step in which a first group of the read write heads of the hard drive are enabled so as to simultaneously write a corresponding first subset of the servo wedges on a corresponding first set of disk surfaces. The first subset of servo wedges are at a corresponding first circumferential location on an individual radial servo track. Then, step two involves disabling the group of heads previously enabled. Step three of the method comprises enabling a next group of read write heads of the hard drive so as to simultaneously write a next subset of the servo wedges on a next set of corresponding disk surfaces. The next subset of servo wedges correspond to the first subset of servo wedges written in step one. Next, in step four, the group of heads previously enabled are disabled. In step five, steps three and four are repeated, if necessary, until a first wedge set has been written. The first wedge set comprises a plurality of corresponding subsets of servo wedges, and the subsets of servo wedges of the typical wedge set are circumferentially spaced from each other along the first radial servo track by a stagger distance. Following step five, step six begins and in which the first group of read write heads of the hard drive are enabled so as to simultaneously write a first subset of the servo wedges of the next wedge set on the first set of corresponding disk surfaces. In step seven, the groups of heads previously enabled in step six are disabled. After step seven, step eight involves enabling the next group of the read write heads of the hard drive so as to simultaneously write the next corresponding subset of servo wedges on the next set of disk surfaces wherein the next corresponding subset of servo wedges fall into the same wedge set affected in step six. In step nine, the group of heads enabled in step eight are disabled. Then, in step ten, steps eight and nine are repeated, if necessary, until a next wedge set has been written. Step eleven comprises repeating, if necessary, steps six through ten for each of the remaining wedge sets on the radial servo track affected in step one. Finally, step twelve comprises repeating, if necessary, steps one through eleven for each of the remaining servo tracks of the plurality of disk surfaces.
In another aspect the method involves writing servo tracks on a hard drive having a plurality of disk surfaces and read write heads, and each disk surface comprises a plurality of servo tracks at a plurality of radial locations. A particular servo track is represented by the variable X, and typical servo track comprises a plurality of servo wedges. The servo wedges are grouped so as to define wedge sets, and a particular wedge set is represented by the variable Z. Each wedge set comprises a plurality of subsets, and a subset comprises at least two servo wedges but less than the total number of servo wedges in the corresponding wedge set. A particular subset is represented by the variable Y. A first step of the method involves setting X, Y, and Z to an initial value. Then, in step two, the heads are positioned to the radial location of the Xth servo track. Next, in step three, a plurality of heads are enabled to write the Yth subset of the Zth wedge set. The method continues in step four in which the plurality of heads previously engaged in step three are disabled. Step five of the method involves incrementing Y to correspond to the next subset of the Zth wedge set. Next, in step six, steps three through five are repeated, if necessary, until the Zth wedge set is complete. Following step six, step seven begins in which Y is reset to equal the initial value. In step eight of the method, Z is incremented to correspond to the next wedge set. Step nine involves repeating steps three through eight, if necessary, until the Xth servo track is complete. Step ten follows step nine, and step ten comprises incrementing X to correspond to the next servo track. Then, in step eleven, Y and Z are reset to the initial value. Finally, in step twelve, steps two through eleven are repeated, if necessary, until the plurality of servo tracks are complete.
Servo writing is often a time consuming process, and manufacturers often cannot afford enough servo writing machines to maximize throughput. As stated, this method involves writing multiple servo wedges simultaneously. Simultaneous writing of servo wedges advantageously expedites the servo writing process and throughput is increased as a result, which likely leads to cost savings.